Automobiles with an electric propulsion system, such as those with hybrid drive system comprising an internal combustion engine, an electric traction motor and an electric battery, as well an pure electric vehicles, typically deploy regenerative braking in order to recover and store the vehicle's kinetic energy for use in propelling the vehicle. This is achieved by using an electric traction motor in reverse, as a generator, to convert rotational kinetic energy from the vehicle's road wheels to electrical energy which is stored in an electrical battery on the vehicle.
Owing to the capacity of typical electrical traction motors and other characteristics of electrical traction systems the regenerative braking systems cannot absorb energy as rapidly as it can be dissipated by a conventional friction braking system, and their ability to absorb energy can vary with operating conditions such as vehicle speed. Consequently a friction braking system is usually also provided, to supplement and provide a back up to the regenerative system, and a brake control system is provided to distribute braking effort between the friction and regenerative systems. The brake control system is usually arranged to distribute braking effort between the two braking systems to maximise energy recovery, whilst maintaining the feel of a conventional friction braking system to the driver.
In practice the amount of energy that is recovered by regenerative braking systems is limited by a driver's driving style. Heavy braking usually requires both regenerative and friction brakes to operate. Whenever the friction brakes are deployed energy is dispersed that might otherwise be recovered.
Embodiments of the present invention seek to address this problem.